LD-QUERY-CONTROL-ALIST

Ld-query-control-alist is an ld special (see ld). The accessor
is (ld-query-control-alist state) and the updater is
(set-ld-query-control-alist val state). Roughly speaking,
ld-query-control-alist is either nil (meaning all queries should be
interactive), t (meaning all should default to the first accepted
response), or an alist that pairs query ids to keyword responses.
The alist may end in either t or nil, indicating the default value
for all ids not listed explicitly. Formally, the
ld-query-control-alist must satisfy ld-query-control-alistp. The
initial ld-query-control-alist is nil, which means all queries are
handled interactively.

When an ACL2 query is raised, a unique identifying symbol is printed
in parentheses after the word ``Query''. This symbol, called the
``query id,'' can be used in conjunction with ld-query-control-alist
to prevent the query from being handled interactively. By ``handled
interactively'' we mean that the query is printed to *standard-co*
and a response is read from *standard-oi*. The alist can be used to
obtain a ``default value'' for each query id. If this value is nil,
then the query is handled interactively. In all other cases, the
system handles the query without interaction (although text may be
printed to standard-co to make it appear that an interaction has
occurred; see below). If the default value is t, the system acts as
though the user responded to the query by typing the first response
listed among the acceptable responses. If the default value is
neither nil nor t, then it must be a keyword and one of the
acceptable responses. In that case, the system acts as though the
user responded with the given keyword.

Next, we discuss how the ld-query-control-alist assigns a default
value to each query id. It assigns each id the first value paired
with the id in the alist, or, if no such pair appears in the alist,
it assigns the final cdr of the alist as the value. Thus, nil
assigns all ids nil. T assigns all ids t.
'((:filter . nil) (:sysdef . :n) . t) assigns nil to the
:filter query, :n to the :sysdef query, and t to all
others.

It remains only to discuss how the system prints text when the
default value is not nil, i.e., when the query is handled without
interaction. In fact, it is allowed to pair a query id with a
singleton list containing a keyword, rather than a keyword, and this
indicates that no printing is to be done. Thus for the example
above, :sysdef queries would be handled noninteractively, with
printing done to simulate the interaction. But if we change the
example so that :sysdef is paired with (:n), i.e., if
ld-query-control-alist is '((:filter . nil) (:sysdef :n) . t), then
no such printing would take place for sysdef queries. Instead, the
default value of :n would be assigned ``quietly''.